During a write operation, a disc drive receives user data blocks from a storage interface circuit in a host computer. The disc drive stores the user data blocks in addressable physical disc blocks on a disc in the disc drive. Generally, the user data blocks and the physical disc blocks are formatted with the same standard block size limit, for example, 512 bytes.
User file sizes on the host will vary, and the storage interface circuit in the host computer divides up user files into one or more user data blocks with the standard size limit. A last user data block associated with a file may be less than the standard size limit. When this last user data block is stored in a physical disc block, there is leftover, unused space in the physical disc block. Because of the block oriented storage method, the leftover, unused space is not accessible for use.
As a result, the amount of data that can be stored on the disc is considerably less than the storage available on the disc, particularly when there are a large number of small user files. Storage capacity has been increased somewhat by compressing files on the host before they are divided into user data blocks and sent to the disc drive, however, this file compression in the host does not make any use of the unused space in a physical block and uses up host processor time. There is a need to reduce the amount of unused, inaccessible space on data storage devices such as disc drives. There is a need to avoid lost host processor time that is used in compressing files.
The problem is not limited to data storage drives. The problem can also arise in other data storage devices (such as integrated circuit data storage devices) that receive user data blocks and that store the received data in storage that is organized into physical data blocks. The problem can arise in magnetic, magneto-optical, optical, ferroelectric and electronic data storage devices when the devices are organized in a block or block-like manner.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.